With the advent of central heating systems and abundantly available and relatively inexpensive fossil fuels, old-fashioned "pot-bellied" stoves which formerly were used to provide heat have fallen into disuse. Central heating systems offer a distinct advantage over individual heating stoves located in each room which a person desires to heat. Furthermore, central heating systems can be hidden away out of view from the rooms in which they supply heat. In addition, such systems, even coal fired systems, are relatively easy to clean and to maintain. As a consequence, up until recently, there has been little interest in wood burning heating stoves, particularly those which are located within the room which is to be heated. This has been true even for remote cabins or cottages since bottled gas or petroleum fuels have been available in abundant quantities for use with the heating plan of such buildings.
At the present time, however, it is becoming abundantly clear that the fossil fuels which have been used to such a great extent over the past few decades are in dangerously short supply. Furthermore, these fuels are obtained from nonreplenishable sources; and at the present rate of consumption, it is readily apparent that other alternatives to the use of these fuels for producing energy must be found. In addition, the costs of fossil fuels have rapidly risen, so that they no longer are the bargain source of energy which they were only a few years ago.
Because of increasing awareness of the finite quantity of fossil fuels available and because of the increasing costs of these fuels, substantial interest is being directed toward finding other sources of energy to replace the fossil fuel consumption which has become so widespread over the past few decades. One source of fuel which is present in large quantities and which is a replenishable source is wood. When forests are properly managed, they produce a continuous supply of wood for various uses, one of which is fuel.
Thus, there now is an increasing interest in wood burning stoves for heating small buildings and remotely located buildings as well as interest in using wood burning stoves in applications where presently fossil fuel central heating systems are commonly employed or as a supplement to existing systems. The wood burning stoves commonly employed, however, generally are extremely inefficient as heating sources. Most of them rely upon radiation and convection currents of air within the room coming into contact with the outside walls of the stove to produce heated air. In such stoves the major portion of the heat produced by the combustion of the wood or other combustible products in the stove is lost with the combustion products out the flue or smoke stack. This is one of the greatest drawbacks of self-contained room size wood burning stoves. In addition, the room itself is not uniformly heated. The region immediately adjacent the stove is too hot, while the more remote corners or sides of the room obtain relatively little heat from the stove.
Some early models of wood burning heating stoves, in attempts to overcome the inefficiency of such stoves, relied upon rather extensive baffles between the upper portion of the combustion chamber and the outlet for the flue in order to force the combustion products to take a tortuous path from the upper portion of the combustion chamber to the flue. This resulted in retention of more heat within the stove and an improvement in radiation of this heat from the stove. The operation, however, is still relatively inefficient and a large amount of heat loss results due to hot air passing out the flue.
To improve these early wood burning stoves resort was made to a double wall along at least a portion of the fire chamber to create an air chamber heated on one side by one of the walls of the fire chamber. An air inlet was provided near the bottom of this air chamber and appropriate air outlets were created near the top. Air rose by convection current through the air chamber and out the outlets. Thus, this air was heated in addition to the air coming in contact with the outside of the stove. To improve efficiency still further, fans or blowers were employed to draw air through the air chamber and over the outer walls of the fire chamber. While the fans did provide improved efficiency, the bulk of the heat generated by the process of combustion still was lost in the flue, as could be evidenced by the fact that the flue pipe of an operating stove is generally too hot to touch.
Another common problem with wood burning stoves is that they may allow smoke to escape into the room or rooms which are being heated, especially when initially starting a fire in the stove. At start up there is often a column of cold air in the flue or chimney. This cold air blanket may initially impede the flow of combustion gases out the flue, causing a back pressure of combustion gases which may then escape into the room.
A problem other than cold air induced backflow is often encountered on start up. Specifically, a fan, which is used to circulate air through the heating stove, will cause cold air to blow around the room until the stove has enough heat to heat the air circulated by the fan. Accordingly, this problem is often avoided by turning the fan on (either manually or by a thermostatic switch) only after the stove is sufficiently heated to heat the air circulated by the fan. However, this creates an undesirable delay between the starting of a fire and the beginning of heated air flow from the stove.
In addition to the foregoing disadvantages, most wood burning stoves are rather obtrusive and unattractive. It is desirable to provide a wood burning stove with an appearance approximately that of a fireplace and useable as a fireplace so that it can perform a function of attractiveness as well as utility in the room in which it is used. In addition, it is desirable to provide a wood burning stove with improved efficiency, so that the greatest portion of the heat generated by the wood or other fuel burned in the stove is utilized to heat the room within which the stove is used.